Hierarchical printed product and composition and method for making the same

ABSTRACT

Disclosed herein are embodiments of a printable composition that can be used to make printed products of a chosen material chemistry that have different levels of porosity within the printed product&#39;s structure Also disclosed herein are embodiments of a printed product that has multiple levels of porosity throughout its structure, which can include a macroscale level of porosity, a microscale level of porosity, a nanoscale level of porosity and any combination thereof. These printed products can be made using a 3-D printer and can be made from a single printable composition without the need to add different structural components during the production process. Also disclosed herein are embodiments of a method for making and using a printed product.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of the earlier filing date of U.S.Provisional Patent Application No. 62/625,901, filed on Feb. 2, 2018;this prior application is incorporated herein by reference in itsentirety.

ACKNOWLEDGMENT OF GOVERNMENT SUPPORT

This invention was made with government support under Contract No.89233218CNA000001 awarded by the U.S. Department of Energy/NationalNuclear Security Administration. The government has certain rights inthe invention.

FIELD

The present disclosure concerns embodiments of a hierarchical printedproduct and embodiments of a composition and method for making the same.

BACKGROUND

Porous materials are ubiquitous in modern industrial civilization andwidely utilized in catalysis, energy systems, separation process,medicine, heat transfer, etc. As these technologies progress forward,sophisticated and efficient synthetic methods have emerged for producingstructures with a nanoscopic structure, high surface area, andengineered material functionality. More specifically, a surge ofexperimental studies on hierarchically porous solids has been observedin the past decade—these materials are designed to possess bothlarge-scale porosity that facilitate fluid transport, with “textured”walls made up of much smaller meso or nanopores with high active surfacearea. This morphology is suited for the host of current technologiesthat rely on intimate contact at solid/fluid interfaces (e.g., batteriesand fuel cells, separation media, heat exchangers, heterogeneouscatalysts, etc.). Minimizing transport-limited behavior in porousstructures remains a challenge in materials science, and while targetedR&D efforts toward new materials with multi-scale features and porosityhas driven rapid progress in academia, there are exceedingly limitedsynthetic techniques that are scalable, manufacturable, and adaptable todifferent designs of either chemical functionality and structure.

SUMMARY

Disclosed herein are embodiments of a printable composition, comprisinga structural precursor component; a polymer precursor component; and aporogenic solvent. In some embodiments, the structural precursorcomponent can comprise a metal or a metal precursor; a polymer or amonomer precursor to the polymer; a pre-ceramic material; a pre-metaloxide; a carbonaceous material or a precursor thereof; or anycombination thereof. Some embodiments of the composition furthercomprise a terminating compound, a reducing agent, an initiator, or anycombinations thereof.

Also disclosed herein are embodiments of a method for making a printedproduct using the printable composition embodiments disclosed herein.Steps of method embodiments of the present disclosure are discussedherein. Also disclosed are embodiments of a printed product comprising astructural component having a combination of macroscale pores and/orchannels and microscale pores and/or channels, or a combination ofmacroscale pores and/or channels and nanoscale pores and/or channels, ora combination of microscale pores and/or channels and nanoscale poresand/or channels, or a combination of macroscale pores and/or channels,microscale pores and/or channels, and nanoscale pores and/or channels.

The foregoing and other objects and features of the present disclosurewill become more apparent from the following detailed description, whichproceeds with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating using a printable compositionas discussed herein to make a printed product wherein a polymerprecursor is used in the printable composition to provide a polymericstructure upon polymerization, which ultimately is decomposed to reveala structure made predominantly of a structural component describedherein.

FIG. 2 is an SEM image illustrating a representative printed productcomprising gold and that comprises three levels of porosity, wherein onelevel is pictured in the image labeled as “A”; a second level ispictured in the image labeled as “B”; and a third level is pictured inthe image labeled as “C.”

FIG. 3 is an SEM image illustrating a representative printed productcomprising silver and that comprises two levels of porosity, wherein onelevel is pictured in the left-most image and the other level is picturedin the zoomed view of the left-most image.

FIGS. 4A and 4B are images illustrating a macroscale level of porositythat be formed in printed product embodiments described herein (FIG. 4A)and the additional levels of porosity present in the macroscale level ofporosity (FIG. 4B).

FIGS. 5A and 5B are images illustrating a macroscale level of porositythat be formed in printed product embodiments described herein (FIG. 5A)and the additional levels of porosity present in the macroscale level ofporosity (FIG. 5B).

FIGS. 6A and 6B are images illustrating a macroscale level of porositythat be formed in printed product embodiments described herein (FIG. 6A)and the additional levels of porosity present in the macroscale level ofporosity (FIG. 6B).

FIGS. 7A and 7B are images illustrating a macroscale level of porositythat be formed in printed product embodiments described herein (FIG. 7A)and the additional levels of porosity present in the macroscale level ofporosity (FIG. 7B).

FIG. 8 is a schematic illustration of a representative process by whichhierarchical printed products can be formed using method embodimentsdescribed herein.

FIG. 9 is an image of a printed product formed using composition andmethod embodiments described herein, which illustrates a printed productbefore and after a processing method that facilitates isotropicshrinkage thereby reducing feature sizes far below the printedresolution (as can be seen by comparing the left-most and middle imageswith the right-most image).

FIGS. 10A-10F provide images of a gold-based printed product madeaccording to a method embodiment of the present disclosure; FIG. 10A isa digital image showing the macrostructure of the gold-based printedproduct; FIG. 10B shows a flow-through device comprising the gold-basedprinted product; FIG. 10C is an SEM image showing pores of thegold-based printed product on a 500 μm scale; FIG. 10D is an SEM imageshowing pores of the gold-based printed product on a 100 μm scale; FIG.10E is an SEM image showing pores of the gold-based printed product on a2 μm scale; and FIG. 10F is an SEM image showing pores of the gold-basedprinted product on a 500 nm scale.

FIGS. 11A-11E provides images of a silica-based printed product madeaccording to a method embodiment of the present disclosure; FIG. 11Ashows the macrostructure of the silica-based printed product; FIG. 11Bshows a zoomed image of the macroscale pores of the silica-based printedproduct; FIG. 11C is an SEM image showing pores of the printed producton a 100 μm scale; FIGS. 11D and 11E shows a second level of porosity inthe product and confirms that this additional level of porosity existson length scales smaller than the macroscale pores.

FIG. 12 is a digital image of a boron carbide-based printed product madeusing a method embodiment of the present disclosure.

FIG. 13 is an X-ray diffraction pattern obtained from analyzing apulverized sample of the boron carbide-based printed product shown inFIG. 12.

FIGS. 14A and 14B are SEM images showing pores of a copper-based printedproduct made according to a method embodiment of the present disclosure,wherein FIG. 14A shows the pores on a 200 μm scale and FIG. 14B showsthe pores on a 5 μm scale.

FIGS. 15A-15C provide images of an iron-based printed product madeaccording to a method embodiment of the present disclosure; FIG. 15Ashows a digital image of the iron-based printed product; 15B is an SEMimage showing pores of the iron-based printed product on a 200 μm scale;and FIG. 15C is an SEM image showing pores of the iron-based printedproduct on a 10 μm scale.

DETAILED DESCRIPTION I. Overview of Terms

The following explanations of terms are provided to better describe thepresent disclosure and to guide those of ordinary skill in the art inthe practice of the present disclosure. As used herein, “comprising”means “including” and the singular forms “a” or “an” or “the” includeplural references unless the context clearly dictates otherwise. Theterm “or” refers to a single element of stated alternative elements or acombination of two or more elements, unless the context clearlyindicates otherwise.

Although the steps of some of the disclosed methods are described in aparticular, sequential order for convenient presentation, it should beunderstood that this manner of description encompasses rearrangement,unless a particular ordering is required by specific language set forthbelow. For example, steps described sequentially may in some cases berearranged or performed concurrently. Additionally, the descriptionsometimes uses terms like “produce” and “provide” to describe thedisclosed methods. These terms are high-level abstractions of the actualsteps that are performed. The actual steps that correspond to theseterms will vary depending on the particular implementation and arereadily discernible by one of ordinary skill in the art.

Unless explained otherwise, all technical and scientific terms usedherein have the same meaning as commonly understood to one of ordinaryskill in the art to which this disclosure belongs. Although methods andcompounds similar or equivalent to those described herein can be used inthe practice or testing of the present disclosure, suitable methods andcompounds are described below. The compounds, methods, and examples areillustrative only and not intended to be limiting, unless otherwiseindicated. Other features of the disclosure are apparent from thefollowing detailed description and the claims.

Unless otherwise indicated, all numbers expressing quantities ofcomponents, molecular weights, percentages, temperatures, times, and soforth, as used in the specification or claims are to be understood asbeing modified by the term “about.” Accordingly, unless otherwiseindicated, implicitly or explicitly, the numerical parameters set forthare approximations that can depend on the desired properties soughtand/or limits of detection under standard test conditions/methods. Whendirectly and explicitly distinguishing embodiments from discussed priorart, the embodiment numbers are not approximates unless the word “about”is recited. Furthermore, not all alternatives recited herein areequivalents.

To facilitate review of the various embodiments of the disclosure, thefollowing explanations of specific terms and abbreviations are provided:

Channel: A fabricated or naturally occurring pathway created in aprinted product described herein through which fluid can flow, whereinthe channel has walls defined by the printed product. In someembodiments, a channel is formed by connectivity of two or more pores.In some embodiments, a channel has two dimensions of limited length andone dimension of unspecified length (e.g., such a channel could traversethe printed product in a tortuous path of unspecified length). In someembodiments, classification of the channel can be defined by thelimiting dimensions. In some embodiments, channels can be macrochannels,microchannels, or nanochannels. The term “macrochannels,” as usedherein, is understood to refer to channels having dimensions greaterthan 1 mm to 100 mm or more. The term “microchannels,” as used herein,is understood to refer to channels having dimensions of greater than 1μm to 1000 μm. The term “nanochannels,” as used herein, is understood torefer to channels having dimensions of from 1 nm or lower to 1000 nm.

Initiator: A compound that is capable of initiating or promoting theformation of one or more radical species and/or ionic species from apolymer precursor component.

Gas-Phase Reagent: A gas that can be used in method embodiments of thepresent disclosure to initiate or otherwise cause a chemical change in astructural precursor component such that the structural precursorcomponent is converted to a structural component that becomes a majoritycomponent of a printed product.

Monomer Unit: A single monomer species, or an oligomer species(comprising one or more monomer species that are the same or different),or any combination thereof, that provides a polymerizable unit thatserves as a polymer precursor component. Solely by way of example,polyethylene glycol diacrylate is a monomer unit comprising an oligomerof ethylene glycol units that can serve as a polymer precursor componentthat can be polymerized to provide a polyethylene glycol polymer.

Polymer Gel: A composition comprising a polymer network formed frompolymerizing a polymer precursor component of a printable composition inthe presence of a porogenic solvent (or “porogen”).

Polymer Precursor Component: A compound that comprises one or morefunctional groups capable of polymerizing to form a polymeric structure,wherein the compound is a separate and distinct component from anystructural precursor component of the printable composition. In anindependent embodiment, the polymer precursor component is notmethylcellulose or poly(vinyl) alcohol.

Polymerization Quenching Compound: A compound that is capable ofpreventing or reducing any undesired polymerization of the polymerprecursor component. In some embodiments, the polymerization quenchingcompound (i) prevents polymerization from extending beyond a treatmentpattern used print a printed intermediate structure, such as bypreventing radical formation in regions not within the treatmentpattern, (ii) prevents polymerization from increasing the thickness ofprinted layers of the printable composition beyond a desired thickness(e.g., thickness above the height of a printing plane along the z-axis),and/or (iii) scavenges radicals to thereby terminate polymerization. Insome embodiments, the polymerization quenching compound can be a radicalscavenger or an absorber compound.

Porogenic Solvent (or Porogen): A solvent in which a polymer precursorcomponent exhibits low solubility such that any resulting polymer (thatis, a polymer obtained from cross-linking and/or otherwise polymerizingthe polymer precursor component) is phase-separated from the solvent,thereby forming pores and/or channels within a printed structure. Inparticular disclosed embodiments, the degree of solubility of thepolymer precursor component in the porogenic solvent influences the poresize and structure. For example, the more soluble the polymer precursoris in the porogenic solvent, the smaller the resulting pore sizes willbe. Exemplary porogenic solvents include, but are not limited to,dimethylformamide, water, dimethyl sulfoxide (DMSO), alcohols, esters,ketones, glycols, aldehydes, hydrocarbons, weak acids, and weak bases.In an independent embodiment, the porogenic solvent is not acetone,chloroform, or dichloromethane.

Pore: One of a plurality of openings or void spaces in a printedstructure or printed product described herein. Pores, as describedherein, are characterized by their diameters. Macroscale pores includelarge pores having diameters ranging from greater than 1 mm to 100 mm ormore. Microscale pores include small pores having diameters ranging fromgreater than 1 μm to 1000 μm. Nanoscale pores include very small poreshaving diameters ranging from 1 nm or lower to 1000 nm. In somerepresentative embodiments, the pores may have diameters ranging from100 μm to 1 mm, or from 100 nm to 1 μm.

Printable Composition: A composition having chemical and/or physicalproperties (e.g., dispersibility, viscosity, flowability, and the like)sufficient to allow the composition to be printed using a 3-D printer orother stereolithographic process.

Printed Intermediate Structure: A structure formed by printing aprintable composition and that comprises (i) a polymer gel and astructural precursor component; or (ii) a polymer gel and a structuralcomponent provided by reaction of the structural precursor component. Inparticular embodiments, a printed intermediate structure is a structureobtained after printing a printable composition and prior to removing apolymer gel.

Printed Product: A structure that comprises a structural componentprovided by a structural precursor component of the present disclosureand that is free of a polymer gel or that is substantially free of apolymer gel, such that only trace amounts of the polymer gel aredetectable in the printed product, with such trace amounts being amountsthat do not lead to deleterious effects on the performance of theprinted product. Solely by way of example, trace amounts of the polymergel can be amounts less than 10 wt % of the printed product, such asless than 8 wt %, less than 6 wt %, less than 4 wt %, or less than 2 wt%.

Structural Precursor Component: A component (or a combination ofcomponents) that is a chemical or physical precursor to thefree-standing structural component of a printed product as describedherein and that is separate and distinct from any polymer precursorcomponent present in a printable composition. In particular embodiments,the structural precursor component itself is not present in the printedproduct and instead is transformed into a structural component thatmakes up the majority of the skeleton of the printed product (or ifpresent is only present in trace amounts relative to the structuralcomponent made therefrom).

Vapor-Phase Reagent: A component that exists in the gas phase at atemperature lower than its critical temperature and that can be used inmethod embodiments of the present disclosure to initiate or otherwisecause a chemical change in a structural precursor component such thatthe structural precursor component is converted to a structuralcomponent that becomes a majority component of a printed product.

II. Introduction

Stereolithography methods typically are limited to producing plastic orpolymeric products. Post-processing has been used in the art to convertprinted plastic or polymeric products to a different material with thesame structure; however, products made using such methods do not havecontrolled surface area and connectivity. That is, they do not havecontrol over more than one length scale.

The present inventors have developed a materials synthesis process forembodiments of a 3-dimensional printed product with engineered porosityacross multiple length scales (referred to herein as a “printed product”and/or a “hierarchical printed product”). Method embodiments describedherein include stereolithography-based methods, which involveincorporating reactive species into printable compositions that may beprinted using commercial stereolithography devices. In some embodiments,these printable compositions are produced by combining cross-linkablepolymer precursor components with specific solvents that result inpartial phase separation of polymerized material (formed frompolymerization of the polymer precursor component) from the solventduring polymerization. This concept of using a polymerizable polymerprecursor component in the presence of a poor solvent acting as a“porogenic solvent” is implemented to make a variety of polymer gelshaving pores and/or channels wherein the pore and/or channel size andvolume may be controlled by tuning the porogenic solvent's affinity forthe monomer, the concentration of porogen, and the use of additives,such as surfactants or other structure-directing agents. In someembodiments, after printing the printable composition, a printedintermediate structure is obtained and various different processingsteps can be used to fill or cast the printed intermediate structurewith material precursors described herein that are present in theprintable composition and that give rise to the materials, such asmetals, ceramics, metal oxides, polymers, carbonaceous materials, andthe like, that make up the final printed product. The inventors are ableto obtain homogeneous incorporation of the structural precursorcomponent within the walls of a 3-D printed intermediate structure thatcan be converted to a final printed product, such as by decomposing apolymer gel of the printed intermediate structure. With such methodembodiments, a structural replica of the printed intermediate structureis provided, which enables a “positive” replica of the 3-D printedintermediate structure, and a “negative” replica of the polymer gelformed within its walls (for example, see FIG. 1).

Not only can a designed product architecture be produced reproducibly,but different levels of porosity and/or channels can be included in theprinted products, which enables the properties of different scaledproducts to be utilized. Additionally, pores of the disclosed printedproducts are interconnected and multimodal and thus are accessiblethroughout macroscale features of the printed products (that is, theyare not isolated or “closed off” from the bulk void space). This synergyof additive manufacturing with macro-, micro-, and/or nano-structuredmaterials can provide printed products with improved capabilities for anarray of current and future technologies.

III. Printable Composition for Forming Printed Product Embodiments

Disclosed herein are embodiments of a printable composition that can beused to form embodiments of a printed product, such as embodiments of ahierarchical printed product. In some embodiments, the printablecomposition embodiments described herein provide an advantage overconventional compositions used for three-dimensional printing of porousstructures because the disclosed composition comprises all componentsthat provide a final printed product that contains multiple differentlevels of porosity spanning multiple length scales. For example,compositions typically used for printing porous products require firstprinting a plastic-based component that serves as a mold on which ametal-based composition is coated, followed by removal of the plasticcomponent to ultimately provide the final metal-based product. As such,these conventional compositions do not include all components used tomake the final product.

In contrast, embodiments of the disclosed printable composition providethe components used to arrive at a final printed product such that allthe components are included in the printable composition and there is noneed to add additional components in subsequent stages. As such, theprinted product can be printed directly without having to add additionalcomponents and/or coatings. Embodiments of the disclosed printablecomposition thus provide at least this advantage over othercompositions. Also, the disclosed printable composition is designed suchthat the various components of the printable composition can be modifiedusing various processing steps to provide a final printed product thathas controlled structural and compositional features. For example,components of the printable composition can be selected such that theywill provide reactive species directly into a printed intermediatestructure. These components and/or reactive species can then be modifiedusing downstream processing techniques, without having to add additionalcompositional components, to provide printed products that havespecifically designed internal structural features, such as controlledpore and/or channel sizes and shapes, controlled porosity levels,controlled pore and/or channel organization, and combinations thereof,that cannot be achieved in the art by other compositions/methods. Assuch, embodiments of the disclosed printable composition and methodprovides the ability to assemble printed products from the inside-outrather than simply overcoating a pre-printed product; a feature that hasnot been achieved to produce free-standing replicas of a desiredchemistry with other printing compositions/methods.

In some embodiments, the printable composition comprises a structuralprecursor component, a polymer precursor component, and a porogenicsolvent. In some embodiments, the printable composition can furthercomprise an initiator and/or a polymerization quenching compoundcomponent. The structural precursor component typically is the componentthat makes up the bulk of the printed product formed from the printablecomposition. The structural precursor can be selected from a metal (or aprecursor thereof), a carbonaceous material (or a precursor thereof), apre-ceramic material, a polymer (or a monomer precursor thereof), apre-metal oxide material, or combinations thereof.

In embodiments where a metal (or precursor thereof) is used as thestructural precursor component, the metal (or precursor thereof) used inthe printable composition can be an alloy, a metal nanoparticle (orplurality of nanoparticles), metal ions in solution, or a non-ionicmetal. Exemplary metals (or precursors thereof) that can be usedinclude, but are not limited to, compounds having metals of Groups 9,10, 11, 12, 13, and 14. In particular disclosed embodiments, the metalis silver, gold, nickel, copper, iron, palladium, platinum, zinc, or acombination thereof. Metal ions in solution can comprise metal saltsthat give rise to a metal species (e.g., reduced metal ions, colloidalmetals, metal nanoparticles, etc.) after a chemical reaction (e.g.,reduction via a reducing agent and/or hydrothermal synthesis methods)and/or heat treatment. Exemplary metal precursors include, but are notlimited to, silver salts (e.g., silver nitrate, silver carbonate, silverhalides, silver cyanide, silver phosphate, and the like); gold salts(e.g., gold(III) bromide, gold(I) chloride, gold(III) chloride,gold(III) chloride hydrate, gold(III) hydroxide, gold(I) iodide,potassium gold(III) chloride, and the like); nickel salts (e.g.,nickel(II) bromide, nickel(II) chloride, nickel(II) fluoride, nickel(II)hydroxide, nickel(II) iodide, nickel(II) nitrate hexahydrate, nickel(II)oxalate dihydrate, nickel(II) sulfate, and the like); iron salts (e.g.,iron(II) bromide, iron(III) bromide, iron(II) chloride, Iron(II) oxalatedehydrate, and the like); palladium salts (e.g., palladium(II) salts,like palladium bromide, palladium chloride, palladium cyanide, palladiumiodide, palladium sulfate, palladium nitrate dehydrate, and the like);platinum salts (e.g., platinum(II) or platinum(IV) salts, like platinumbromide, platinum (II or IV) chloride, platinum iodide, platinumcyanide, and the like); copper salts (e.g., copper(I) or copper(II)salts, such as copper(I or II) bromide, copper(I or II) chloride, copperfluoride, copper iodide, copper nitrate, copper sulfate, copperthiocyanate, and the like); and zinc salts (e.g., zinc bromide, zincchloride, zinc cyanide, zinc fluoride, zinc methacrylate, zinc nitrate,zinc iodide, and the like).

Structural precursor components comprising a metal precursor can alsocomprise a suitable solvent that is capable of solubilizing the metalprecursor, such that it can be printed using a stereolithographicprocess. In some embodiments, the amount of the metal precursor used canselected based on the type of product that is desired. For example, inembodiments where the majority of the final printed product's structureis metal-based, large concentrations of the metal precursor (e.g.,stoichiometric amounts and/or an amount that results in a saturatedsolution of the metal precursor in the solvent) can be used. In someembodiments, lower amounts of the metal precursor component can be used(e.g., less than stoichiometric amounts and/or amounts where a solutionof the metal precursor is not saturated).

In yet some additional embodiments, a combination of two or more metalprecursors can be used in tandem, such as a combination of silver andgold precursors. In some such embodiments, one of the metal precursorscan be used to provide an additional layer of porosity within the finalprinted product, which can result from a de-alloying interaction betweena combination of the two or more metals (or precursors thereof). In anexemplary embodiment, a silver precursor can be used in combination witha gold precursor to provide a gold-based printed product having threedifferent levels of porosity (see, for example, FIG. 2). In suchembodiments, the pores arise from the printed intermediate structureitself, the decomposition of the polymer gel, and the de-alloying of theAg/Au alloy either by free corrosion in solution or by electrochemicalmethods (in order of largest to smallest in size). In such embodiments,the starting alloy composed of Ag and Au metal can comprise 20-50 at %Au (such as 20 at % to 36 at % (or higher) Au, or as between 22 at % and26 at % (or higher) Au) to permit the formation of continuous nanoscalepores. In some embodiments of a product comprising a combination of goldand silver, the method used to make the product provides the ability toavoid formation of a dense silver layer formed around the pores, whichcan prevent suitable gold deposition. Because method embodiments of thepresent disclosure are able to avoid this silver layer formation aroundthe pores, products exhibiting contamination (such as in the form ofresidual CI contamination) are avoided. Such contaminated products donot exhibit accessible interior pores and thus can deleterious affectpost-processing steps; thus, at least one advantage of the presentlydisclosed product and method embodiments is to avoid this undesirableoutcome.

In embodiments where a carbonaceous material is used as the structuralprecursor component, the carbonaceous material can include graphite,graphene, and amorphous carbon; or it can be formed from a carbonaceousprecursor, such as resorcinol and/or formaldehyde, furfuryl alcohol andthe like (used either with or without a corresponding polymerizationcatalyst, such as sodium carbonate, oxalic acid, and the like).

In embodiments where a polymer (or monomer precursor thereof) is used asthe structural precursor component, the polymer can be selected frompolyimide, polyacrylonitrile, polydicyclopentadiene, polybenzoxazine,and the like. In additional embodiments, a monomer precursor of suchpolymers can be used, such as an imide monomer, an acrylonitrilemonomer, a dicyclopentadiene monomer, a benzoxazine monomer, or anycombinations thereof.

In embodiments where a pre-ceramic material is used as the structuralprecursor component, the pre-ceramic material can be used to form aprinted product comprising a ceramic material, which is produced fromthe pre-ceramic material upon exposure to a catalytic hydrolysis step,removal of a polymer gel, and/or a high temperature treatment. Thepre-ceramic material can comprise silicon (e.g., a silicon alkoxide,such as tetraethyl orthosilicate), titanium, boron (e.g., boric acid),aluminum, zirconium, or the like. In some embodiments, the ceramicmaterial made from such pre-ceramic materials can comprise silica, SiC,SiOC, SiCN, Si₃N₄, TiC, boron nitride, boron carbide, aluminum nitride,zirconia, and the like.

In embodiments where a pre-metal oxide is used as the structuralprecursor component, the pre-metal oxide can comprise a metal (or saltthereof) belonging to Group 4, 5, 7, 8, 9, 10, 11, or 12 of the periodictable (or a combination of any such metals). In some embodiments, thepre-metal oxide material can be converted to a metal oxide componentthat makes up the skeleton of the printed product upon removal of thepolymer gel of the printed intermediate structure, wherein the metaloxide can be selected from TiO₂, MnO₂, SiO₂, SnO₂, ZrO₂, ZnO, NiO,BaTiO₂, ZnTiO₃, CuTiO₃, Fe₂O₃, Fe₃O₄, Co₃O₄, V₂O₅, CuO, and the like.Exemplary pre-metal oxide compounds include any metal-containing saltthat can be thermally decomposed to a corresponding oxide or that can bechemically converted to an oxide using a vapor-phase reagent, agas-phase reagent, or a combination thereof. In some embodiments, thepre-metal oxide can include, but is not limited to a titanium oxideprecursor (e.g., TiCl₄, Ti[OCH(CH₃)₂]₄, and the like); a cobalt oxideprecursor (e.g., Co(NO₃)₂.H₂O, CoCl₂ and the like); a zirconium oxideprecursor (e.g., ZrOCl₂.8H₂O, Zr(NO₃)₄, and the like); a nickel oxideprecursor (e.g., Ni(NO₃)₂, NiCl₂, a Ni(II)bis(phosphine) complex, aNi(0) complex, NiCp₂, and the like); or a tin oxide precursor (e.g.,SnCl₂, SnI₄, Sn(acac)₂, or the like). In some such embodiment, the metaloxide can be obtained from the pre-metal oxide component in situ byexposing a printed intermediate structure comprising the pre-metal oxideto water, a vapor-phase reagent (e.g., water vapor), a gas-phasereagent, or a combination thereof.

The polymer precursor component of the printable composition comprisesone or more monomer units, wherein each monomer unit can be the same ordifferent. Each monomer unit of the polymer precursor component can be asingle monomer species (which can be the same [but with differentpolymer weights]), or an oligomer species (which can comprise a mixtureof monomer species, which can be the same [but with different polymerweights]), or a mixture thereof. The monomer units typically comprise atleast one, or two, or three, or four, or five polymerizable functionalgroups (e.g., functional groups that can be cross-linked and/or that canform radicals and/or ions upon exposure to light and/or heat). Suchpolymerizable functional groups include, but are not limited to, adouble bond, an epoxide, an alkylene oxide, an isocyanate, and the like.In some embodiments, the polymer precursor component comprises one ormore acrylic monomers suitable for use in stereolithography. Inparticular disclosed embodiments, the polymer precursor component can beselected from acrylate-containing monomers (such as, but not limited to,polyethylene glycol diacrylate [e.g., PEG(600)diacrylate], polyesteracrylate, urethane acrylate, epoxy methacrylate, trimethylolpropaneethoxylate triacrylate, and the like, and including any combinationsthereof) or vinyl group-containing monomers (such as, but not limitedto, divinyl benzene, divinyl sulfone, divinyl oxybutane, and the like,and including any combinations thereof) that are easily polymerized withlight.

The initiator component can comprise a compound that is capable ofpromoting polymerization of the polymer precursor component, such as byinducing ionic polymerization and/or radical polymerization. In someembodiments, the initiator component can comprise a cationic radicalinitiator (e.g., an onium salt, such as an iodonium salt, a sulfoniumsalt, or a combination thereof; an organometallic complex, such as aferrocinium salt, or a pyridinium salt; or a combination thereof), or afree radical initiator (e.g., a benzophenone, a xanthanone, a quinone, abenzoin ether, an acetophenone, a benzoyl oxime, an acylphosphine, or acombination thereof). In particular disclosed embodiments, the initiatorcomponent can be selected frombis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide,2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone,2-hydroxy-2-methylpropiophenone,2-methyl-4′-(methylthio)-2-morpholinopropiophenone,[4-[(2-Hydroxytetradecyl)oxy]phenyl]phenyliodoniumhexafluoroantimoniate, or the like and including any combinationsthereof. The amount of the initiator component that is used can rangefrom 0.001 wt % to 10 wt % (based on the mass of the monomer used toprovide the monomer unit of the polymer precursor component or based onthe total mass of the polymer precursor component), such as 0.1 wt % to5 wt %, or 0.5 wt % to 1.5 wt %. In some embodiments, the initiator canbe included at an amount that is 1% based on the mass of monomer used toprovide the monomer unit of the polymer precursor component (or, in someembodiments, the total mass of the polymer precursor component). Forexample, assuming the monomer has a density of 1 g/mL, 10 mg of theinitiator would be dissolved per 1 mL monomer used to provide themonomer unit of the polymer precursor component. In other embodiments,an example would be that for every 1 g of the polymer precursorcomponent that is used, the initiator can be used in an amount of 0.1 g.

The printable composition also can comprise a polymerization quenchingcompound, which can be selected from a compound that is capable ofpreventing or reducing any undesired polymerization of the polymerprecursor component (e.g., such that polymerization does not extendbeyond the treatment pattern being used to print the product and/or suchthat the thickness of printed layers of the printable composition iscontrolled to be a particular desired thickness). In some embodiments,the polymerization quenching compound can be selected from a radicalscavenger or an absorber, such as an azo-containing compound (e.g., anazo dye), or a compound capable of terminating ionic polymerization. Insome embodiments when the polymerization quenching compound is a dye,the dye can competes for absorption of the incident light, preventingthe formation of free radicals in areas where polymerization is notdesired. In some embodiments, the polymerization quenching compound canbe a dye, such as an azo-containing dye like a SUDAN® dye (e.g., SUDAN®I, SUDAN® II, SUDAN® III, etc.) or other visible- or UV-absorbing dyesuch as Oracet Yellow, Orasol Orange, and the like. In some embodiments,the amount of the polymerization quenching compound that can be usedranges from 0.001 wt % to 1 wt % based on the mass of the monomer usedto provide the monomer unit of the polymer precursor component, such as0.01 wt % to 0.1 wt %, or 0.1 wt % to 0.3 wt %. In some embodiments, thepolymerization quenching compound is used in an amount that is 0.2 wt %based on the mass of the monomer used to provide the monomer unit of thepolymer precursor component.

The porogenic solvent (or “porogen”) is used to generate porosity in theprinted product and typically provide the largest scale pores and/orchannels present in the printed product (e.g., macroscale pores and/orchannels). In some embodiments, the porogenic solvent can be selectedfrom a solvent in which a polymerized polymer precursor component isminimally soluble. In some embodiments, the porogenic solvent isdimethylformamide, DMSO, water, an alcohol (such as ethanol, pentanol,hexanol, isopropanol, and like), a hydrocarbon (such as undecane,dodecane, and the like), an acid, a base (such as boric acid and thelike), or any combinations thereof. In particular embodiments, the acidand/or base is a weak acid and/or weak base such that the acid and/orbase is not so concentrated that it deleteriously interferes with aprinting process and/or chemically degrades components of the printablecomposition. Solely by way of example, concentrated acids, such asconcentrated nitric or sulfuric acid, are typically not considered weakacids unless they have been diluted to a lower concentration (e.g.,lower than 10M, such as 8M or lower, 4M or lower, 2M or lower, or lessthan 1M. In some embodiments, the porogenic solvent also is selectedbased on its ability to reduce a metal precursor component to a metalion. However, in some other embodiments, a separate reducing agent canbe used to promote reduction of a metal precursor. In embodiments wherethe porogenic solvent is used to promote reduction of a metal precursor,the amount of the porogenic solvent that is used can be selected so asto provide a particular ratio of porogenic solvent to metal precursor.In additional embodiments, the amount of the porogenic solvent can beselected based on the amount of the monomer used to provide the monomerunit of the polymer precursor component that is used. In some particularembodiments, the porogenic solvent is present in an amount ranging from15-85% by volume, such as 20-50% by volume, or 20-30%. In embodimentsusing a reducing agent, the reducing agent is selected to be a chemicalspecies that can reduce metal ions when a metal precursor is used as thestructural precursor component. Exemplary reducing agents include, butare not limited to, sodium citrate, sodium hypophosphite, formaldehyde,ascorbic acid, sodium borohydride, hydrazine, and the like.

The particular components of the printable composition described abovecan be included together in separate compositions that are then mixedtogether to form the printable composition. In some embodiments, a firstsolution comprising a porogenic solvent can be made. In suchembodiments, the first solution can further comprise an initiator and/ora polymerization quenching compound. In some embodiments, the firstsolution can further comprise a reducing agent. In some embodiments, asecond composition can be used, which comprises the polymer precursorcomponent. The second composition can, but need not, include a solvent.A third composition also can be used, which comprises a solution of thestructural precursor component. In some embodiments, the thirdcomposition can comprise a metal precursor solution, a polymer (ormonomer thereof) solution, a pre-ceramic solution, a carbonaceousmaterial solution (or a carbonaceous material precursor solution), ametal oxide precursor solution, or any combination thereof. Thesedifferent compositions can be modified either in terms of the componentsincluded within each composition or in terms of the order in which thecompositions are combined, depending on the materials utilized whenforming the printable composition. In some embodiments, the compositionsare combined in an order that avoids forming an emulsion and/or thatavoids the different compositions from separating in the printablecomposition. In some embodiments, the third solution can be combinedwith the porogenic solvent prior to adding the polymer precursorcomponent. In yet additional embodiments, the structural precursorcomponent can be dissolved in the porogenic solvent prior to adding thepolymer precursor component. Solely by way of example, in someembodiments using a metal precursor as the structural precursorcomponent, the first composition can be made using the initiator, thepolymerization quenching compound, and the porogenic solvent. This firstcomposition is then combined with a second composition comprising apolymer precursor component. This mixture of the first composition andthe second composition is then combined with a third composition, whichcomprises the metal precursor solution. In such exemplary embodiments,the first composition, second composition, and third compositions arecombined at a ratio of 4:2:1 (first composition:second composition:thirdcomposition).

In some embodiments, the volume of porogen used corresponds to thevolume available to add other reactants and precursors to the printedintermediate structure as the other volume is already occupied by thepolymer formed from the polymer precursor component. Solely by way ofexample, if the polymer precursor component is used at 25%, then theremainder of the volume (e.g., 75%) is made up of the porogenic solventand any precursors dissolved or combined with the porogenic solvent.Solely as a representative example, a carbonaceous material can be usedto forms the skeleton of the printed product. In this representativeembodiment 25% by volume poly(ethylene glycol) diacrylate (e.g., MW250), which acts as the polymer precursor component is combined with 75%by volume water (which acts as the porogenic solvent) and formaldehydesolution with dissolved resorcinol (which acts as the structuralprecursor component). In this representative embodiment, theinitiator/absorber concentration relative to mass of the monomer unit(poly(ethylene glycol) diacrylate) that provides the polymer precursorcomponent is 1% and 0.18%, respectively.

In an independent embodiment, if the printable composition comprises apolyethylene glycol monomer (e.g., a polyethylene glycol diacrylate,such as polyethylene glycol diacrylate with a molecular weight of 600 or258), phenylbis(2,4,6-trimethylbenzoyl)phosphineoxide (also known asIRGACURE® 819), 1-phenylazo-2-naphthol (also known as SUDAN® 1), andisopropanol, pentanol, hexanol, and dibutyl phthalate (individually orall four in combination) then the printable composition does notcomprise silver or silver nitrate without further comprising a secondmetal or metal precursor (e.g., gold or a precursor thereof).

In another independent embodiment, if the printable compositioncomprises a combination of resorcinol, formaldehyde, water, polyethyleneglycol monomer (e.g., a polyethylene glycol diacrylate, such aspolyethylene glycol diacrylate with a molecular weight of 600 or 258),phenylbis(2,4,6-trimethylbenzoyl)phosphineoxide, and1-phenylazo-2-naphthol, then the resorcinol, formaldehyde, and watermake up a volume % of the composition that is not, or is other than,80%; and the polyethylene glycol monomer,phenylbis(2,4,6-trimethylbenzoyl)phosphineoxide, and1-phenylazo-2-naphthol make up a volume % of the composition that isnot, or is other than 20%.

IV. Printed Product Embodiments

Printed product embodiments described herein comprise athree-dimensional structure that can comprise one or more levels ofporosity, and typically two or more levels of porosity. In someembodiments, the printed product embodiments described herein have athree-dimensional structure that comprises two, three, four, five, ormore levels of porosity throughout the structure. By “different levelsof porosity” it is meant that the printed product can comprise regionshaving nested levels of porosity. Solely by way of example, a printedproduct as described herein can comprise a three-dimensional “macro”structure wherein structure features of the printed product definemacropores and/or macrochannels. This “macro” structure can furthercomprise regions with additional levels of porosity and/or channels,such as regions comprising micropores, microchannels, nanopores,nanochannels, and any combinations thereof. In some embodiments, theregions can comprise microporous and/or microchannel regions, whichthemselves include nanoporous and/or nanochannel regions. An image of anexemplary product comprising multiple different levels of porosity isshown by FIG. 2. As shown by the insert of SEM image “A” in FIG. 2(image “A”), the product comprises a macro structure having alattice-based configuration. This macrostructure (illustrated as SEMimage “A” in FIG. 2) includes, within regions of the lattice-formingregions, an additional level of porosity as illustrated by SEM image “B”of FIG. 2. The pores of this region are on the microscale. Further, thismicroscale porous region itself includes an additional level of porosityas can be seen by SEM image “C” of FIG. 2. The pores of this region areon the nanoscale.

An additional embodiment of a product described herein is shown in FIG.3. The product of FIG. 3 comprises two levels of porosity; a first levelof porosity is shown in SEM image A of FIG. 3, which comprises amacroscale level of porosity. Regions of the product shown in SEM imageA of FIG. 3 further include a microscale level of porosity, asillustrated in SEM image B of FIG. 3. Additional embodiments of theprinted product having different levels of porosity are illustrated inFIGS. 4A, 4B, 5A, 5B, 6A, 6B, 7A and 7B. These images illustrateconfigurations of the macro structure of the product (FIGS. 4A, 5A, 6A,and 7A) and also show SEM images (FIGS. 4B, 5B, 6B, and 7B), whichillustrate additional levels of porosity within the macro structure ofthe product (e.g., micro and nanoscale porous regions).

In some embodiments, pores present in the product embodiments describedherein can be macroscale pores, microscale pores, nanoscale pores, andany combination thereof. In some embodiments, the product can comprise agradient of pores such that pore size (e.g., pore diameter) decreases orincreases along an axis of the product. In some embodiments, productembodiments can comprise channels, such macrochannels, microchannels,nanochannels, and any combination thereof. In some embodiments, theproduct embodiments can comprise a mixture of such pores and channels.

The product embodiments disclosed herein can be metal-based products,polymer-based products, ceramic-based products, carbonaceousmaterial-based products, and combinations thereof. In some embodiments,products comprising multiple levels of porosity of a mixture of metalscan be made, such as products comprising hierarchical levels of porositycomprising gold and silver. In some embodiments, the printed productcomprises gold, silver, silica, boron carbide, copper, iron, carbon, orcombinations thereof. In particular embodiments, the printed product isfree of (or substantially free of) and polymer gel or polymer precursorcomponent from the printable composition.

In some embodiments, the components that make up the printed product canbe determined using elemental analysis techniques, such as energydispersive X-ray spectroscopy (EDS), X-ray diffraction analysis (XRD),and the like. Also, the size of pores and/or channels present in theprinted product can be determined using scanning electron microscopy(SEM).

V. Method of Making Printed Product Embodiments

Disclosed herein are embodiments of a method for making a printedproduct, such as a hierarchical printed product. In some embodiments,the method comprises preparing a first composition comprising aninitiator, a polymerization quenching compound, a porogenic solvent, areducing agent or any combination thereof. The method can furthercomprise preparing a second composition comprising a solution or neatcomposition of a polymer precursor component. The method can furthercomprise preparing a third composition comprising a structural precursorcomponent. In yet some additional embodiments, the method comprisescombining a first composition comprising an initiator, a polymerizationquenching compound, a porogenic solvent, a reducing agent or anycombination thereof with a polymer precursor component and a structuralprecursor component, in any order, to form a printable composition. Inyet additional embodiments, the method can comprise forming a printablecomposition by combining an initiator, a polymerization quenchingcompound, a porogenic solvent, a polymer precursor component, and astructural precursor component in any order that avoids forming anemulsion or that avoids separation of one or more of the components. Inyet additional embodiments, the structural precursor component can beadded as a separate solution after printing a printed intermediatestructure with a printable composition comprising the polymer precursorcomponent. Representative embodiments can include copper-based printedproduct embodiments and iron-based printed product embodiments. In someembodiments, the components used to form the printable composition canbe provided as pre-formed solutions that are simply mixed together in asuitable order. In yet additional embodiments, the components can bepre-mixed to form a printable composition that can be used without theuser having to pre-form and/or pre-mix the various components of theprintable composition.

The method can further comprise loading the printable composition into a3-D printer, such as by placing a pre-prepared cartridge comprising theprintable composition into the printer. The settings of the 3-D printercan be selected to provide a printed intermediate structure having anydesired shape, thickness, and/or porosity. In some embodiments, suchsettings can involve selecting a particular energy source and intensity(e.g., a light source having an intensity suitable to promotepolymerization of the polymer precursor component and/or a heat sourcehaving a temperature suitable to promote polymerization of the polymerprecursor component), a particular printing orientation (e.g., selectinga printer with a bottom-up or a top-down orientation), etc. In someembodiments, the printer settings are selected so as to provide aprinted intermediate structure, such as a printed intermediate structurehaving a lattice structure, a gyroid structure, or the like, using theprintable composition. As printed layers of the printable compositionare sequentially deposited to build the printed intermediate structure,the layers are exposed to the energy source, which polymerizes thepolymer precursor component to form a polymer gel in which thestructural precursor component is suspended. In other embodiments, theprintable composition layers can be printed to provide a printedintermediate structure that is then exposed to a composition comprisinga structural precursor component.

Once a printed intermediate structure has been formed using theprintable composition, the printed intermediate structure can be furthertreated to remove any residual printable composition that may be presentwithin pores of the printed intermediate structure and/or on anyinterior or exterior surfaces of the printed intermediate structure andthat includes any non-polymerized polymer precursor. In someembodiments, any residual printable composition can be removed bywicking away the printable composition, such as by placing the printedintermediate structure in contact with an absorbing medium, such as acloth or paper capable of absorbing fluid. In some embodiments, theprinted intermediate structure also can be rinsed with a rinsingcomposition so as to ensure that the pores and/or channels formed withinthe printed intermediate structure are not blocked and/or filled. Insome embodiments, it is desirable to have all the pores and/or channelsaccessible at all (or substantially all) points of the printedintermediate structure. The rinsing composition can comprise a solvent(e.g., a porogenic solvent that is the same or different from that usedin the printable composition), a stabilizing component, or a combinationthereof. In particular disclosed embodiments, the rinsing compositioncomprises a 3:1 mixture of the solvent to stabilizing component. Thestabilizing component can be used in embodiments where it is desirableto stabilize (e.g., to prevent any further reaction and/or growth of thestructural precursor) any of the structural precursor components thatmight be present on the outer surfaces of the printed intermediatestructure. Solely by way of example, a stabilizing component, such aspolyvinyl pyrrolidone (or “PVP”), can be used to prevent growth of somemetal particles that might be on the exterior of the printedintermediate structure so that the pores of the printed intermediatestructure are not blocked and rendered inaccessible from the outside ofthe printed intermediate structure. In some embodiments, the printedintermediate structure can be suspended (or dipped) in the rinsingcomposition or the rinsing solution can be deposited on the printedintermediate structure. In some embodiments, the amount of the rinsingsolution that is used can be selected based on the size, shape, and/orporosity of the printed intermediate structure. In particular disclosedembodiments, the rinsing composition is used in an amount that allowsthe exterior surface and internal pores of the printed intermediatestructure to be contacted by the rinsing composition. Solely by way ofexample, a printed intermediate structure that is 1 cm³ in size and thathas pores with a 250 μm diameter can be contacted with 1 to 2 mL (ormore) of the rinsing composition.

Embodiments of the method can further comprise exposing the printedintermediate structure to a coating fluid, such as an oil (e.g.,silicone oil or the like). This exposure step is used to coat theexterior of the printed intermediate structure and any internal poresand surfaces in preparation for any subsequent reaction steps. Thecoating fluid is selected to be immiscible with any remaining fluid thatmay be present in the printed intermediate structure (e.g., theporogenic solvent and/or solvents used to provide the structuralprecursor component). The coating fluid minimizes solvent evaporationand associated precursor transport (e.g. of metal ions) from innerregions of the printed intermediate structure to the exterior surfacesof the printed intermediate structure. In some embodiments, the printedintermediate structure can be placed in a container to which the coatingfluid is then added in an amount sufficient to coat the printedintermediate structure. In some embodiments, a coating fluid is notneeded.

In some embodiments, the method further comprises heating the printedintermediate structure. In embodiments using a coating fluid, theprinted intermediate structure is heated after it has been exposed tothe coating fluid. In such embodiments, the coating fluid can still bepresent. The heating step can be optional and whether it is used or notdepends on the structural precursor component used in the printablecomposition. In embodiments using a heating step, the heating step canpromote reduction of the structural precursor component to provide thematerial that becomes the structural base for the printed product. Forexample, in embodiments comprising a metal precursor, the heating stepis used to reduce metal ions of the metal precursor in the presence ofthe additional components present in the printed intermediate structure(e.g., the porogenic solvent and/or any solvent used to dissolve themetal precursor component). In such embodiments, heating is carried outat a temperature and for a time sufficient to promote reduction of metalions of the metal precursor. Solely by way of example, a printedintermediate structure comprising a silver-containing metal precursor(e.g., silver nitrate and silver ions produced therefrom) can be heatedat 70° C. (or higher) for 4 hours or more to reduce any silver ions thatare present. Without being limited to a single theory, it currently isbelieved that the following reaction may take place during the heatingstep of exemplary embodiments using a silver-containing metal precursor,DMF as the porogenic solvent, and water (used with the silver-containingmetal precursor):HCONMe₂+2Ag⁺+H₂O→2Ag⁰+Me₂NCOOH+2H⁺.

In some embodiments, the method can comprise exposing the printedintermediate structure to an alcohol (e.g., ethanol) to remove thecoating fluid and any residual components still present in the printedintermediate structure (e.g., any porogenic solvent, heat treatmentby-products, and the like). The printed intermediate structure can thenbe dried. A drying step can involve affirmatively removing the alcohol(e.g., by using heat or passing air or an inert gas over the printedintermediate structure), or it can be removed by simply allowing thealcohol to evaporate. At this stage of some method embodiments, theprinted intermediate structure can comprise a composite materialcomprising the polymer gel formed from the polymer precursor componentand the structural material formed from the structural precursorcomponent that becomes the base material of the printed product. A firstlevel of porosity can be obtained in this printed intermediate structureby decomposing the polymer gel present in the printed intermediatestructure. In some embodiments, the polymer gel can be decomposed byexposing the printed intermediate structure comprising the compositematerial to an energy source, such as a heat source. In yet additionalembodiments, the polymer gel can be decomposed using a chemicaltreatment. Upon decomposition of the polymer gel, additional poresand/or channels are provided in the printed intermediate structure,which were previously spaces within the printed intermediate structurethat were occupied by the polymer gel prior to decomposition. In someembodiments, the energy source is a heat source capable of heating theprinted structure at a temperature ranging from greater than roomtemperature to 700° C., such as 50° C. to 650° C., or 100° C. to 600°C., or 100° C. to 550° C., or 100° C. to 500° C., or 100° C. to 475° C.In some embodiments, the temperature can be increased at a particularrate for a particular time. For example, the energy source can beoperated/programmed to increase the temperature by X ° C./minute,wherein X can range from greater than 0 to 20, such as 1 to 15, or 1 to10, or 2 to 8, or 4 to 6. In particular embodiments, the temperature isincreased by 2° C./minute. In some embodiments, exposing the printedintermediate structure to an energy source can also promote conversionof the structural precursor component to the structural material thatbecomes the base of the printed product. For example, the energy sourcecan promote sintering of metal species (e.g., nanoparticles or the like)formed from the metal precursor component present in the printedintermediate structure so that particles (e.g., nanoparticles) of themetal species are fused together to provide a metal material that formsthe base of the printed product.

In some embodiments, the method can further comprise exposing theprinted intermediate structure to a flowing inert gas (e.g., Ar, N₂,etc.) simultaneously with heating. In additional embodiments, the methodcan further comprise exposing the printed product to flowing air afterthe polymer gel has been decomposed so as to remove any residualdecomposed polymer gel and/or other chemical contaminants. Upon removalof the decomposed polymer gel, a printed product can be obtained thatcomprises a first level of porosity achieved by printing the printablecomposition and a second (typically smaller) level of porosity achievedby removing the polymer gel and leaving behind the structural componentformed from the structural precursor. In some embodiments, the size ofthe printed product can change as the polymer gel is decomposed. Inparticular disclosed embodiments, isotropic shrinkage of the printedproduct can take place such that a first level of porosity of theprinted product can be obtained that cannot be achieved usingconventional porous printing techniques with 3-D printers. As such, thedisclosed method provides engineered printed products that haveporosities and internal structural details that cannot be obtained withconventional polymer compositions and 3-D printing. Another feature ofthe disclosed method is that by modifying the concentration of thestructural precursor component to the polymer precursor component, thesize of the printed product (including the pore volume of the printedproduct) can be tuned as desired. Size and pore volume also can be tunedby modifying the conditions used for the heating step used to decomposethe polymer gel (e.g., by modifying the rate of temperature increase ofthe energy source, the starting and/or ending temperature of the energysource, the length of time of heating, and any combination thereof).

In yet additional embodiments, the method steps described above (or anycombination thereof) can be used in combination with additional methodsteps that are used to provide one or more additional levels of porosityin the printed product. In some embodiments, an additional method stepcan comprise exposing the printed intermediate structure to anotherstructural precursor component after exposing the printed intermediatestructure to the alcohol used to remove the coating fluid and anyresidual components still present in the printed intermediate structure,as discussed above. For example, the dried printed intermediatestructure obtained after removing the alcohol can be exposed to acomposition comprising the additional structural precursor component.Solely by way of example, this composition can comprise a solution of asecond metal precursor that is different from the metal precursor usedto form the printed intermediate structure. In some exemplaryembodiments, a composition comprising a gold-containing precursor (e.g.,HAuCl₄ and HAuCl₄.3H₂O) and ethanol and/or water is used. The printedintermediate structure can be immersed or otherwise coated with thiscomposition such that the exterior and internal surfaces of the printedintermediate structure are wetted with the composition. The printedintermediate structure can remain coated/immersed in this compositionfor a suitable amount of time to allow the additional structuralcomponent to deposit on and within the printed intermediate structure tothereby provide a modified printed intermediate structure. In someembodiments, the printed intermediate structure is immersed in thecomposition for more than 1 hour, such as 2 or more hours, or 2 hours to24 hours, or 2 hours to 16 hours, or 2 hours to 10 hours. Subsequently,the modified printed intermediate structure can be exposed to an alcoholrinse. Any number of rinsing steps can be used, but preferably themodified printed intermediate structure is rinsed until the effluentliquid is colorless. The modified printed intermediate structure is thendried (either affirmatively or naturally as described above). However,in some embodiments, if a gold-containing precursor with sufficientsolubility so as to form a solution is available, then thegold-containing precursor could be mixed with another metal precursorcomponent (e.g., a silver precursor component) to form an initial mixedmetal solution that can be used in the printable composition. In yetsome additional embodiments, the printed intermediate structure can beexposed to a vapor-phase reagent, a gas-phase reagent, or anothercatalyst, or a combination thereof that promotes a chemical change inthe structural precursor component (e.g., polymerization, oxideformation, alloying, hardening, or the like) that facilitates conversionof this component to the structural material of the printed product thatserves as a majority component of the printed product. Other catalyststhat can be used can include metal catalysts (e.g., titania, copper, orother metal catalysts), epoxy-based polymer catalysts (e.g.,epichlorohydrin, propylene oxide or similar reagents that can act asreducers, cross-linkers or hardeners), or a volatile hardener catalyst(e.g., a thiol or amine compound), which can provide an epoxy polymer.In some embodiments, the vapor-phase reagent, the gas-phase reagent, orthe combination thereof can promote in situ generation of the structuralcomponent that makes up the printed product prior to removing thepolymer gel.

After drying, the modified printed intermediate structure can be exposedto a heat treatment step as described above for decomposing the polymergel. In embodiment comprising two different metal precursors asstructural components, the heat treatment step not only degrades thepolymer gel, but it also alloys (or “fuses”) together particles of thetwo metals formed from the two different metal precursor components,thereby forming a free-standing printed product made up of the twodifferent metals. As such, the heating step also can be used to promotea chemical change in structural precursor component. A de-alloying stepcan then be performed to selectively remove one of the metal componentsfrom regions of the printed product to thereby leave behind anotherlevel of porosity within the printed product. The de-alloying step cancomprise performing an electrochemical reaction such that one of themetal species is leached from the printed product, or it can compriseexposing the printed product to an etchant, such as an acid toselectively leach one of the metal species from the other. In anexemplary embodiment, an alloyed printed product comprising alloyedsilver and gold can be exposed to an acid, such as nitric acid, to leachsilver from regions of the printed product, which leaves behind poresformed in the gold. In yet additional embodiments, the printed productcan be thermally annealed to modify the pore size of pores formed in thegold and/or to improve the strength of the printed product. Thesenanoporous gold regions of the printed product form an additional levelof porosity within the printed product. In particular disclosedembodiments using a combination of gold and silver, the gold componentcan be present in an amount ranging from 20 to 40 atomic %, with thesilver component making up the remaining atomic %.

FIG. 8 provides an illustrative schematic of representative stages ofprinted product formation. In this representative example, a printedstructure formed from 3-D printing of a printable composition describedherein is illustrated as printed structure 800. As shown in FIG. 8, thisprinted structure 800 comprises regions that include a mixture of apolymer gel, a porogenic solvent, and a structural precursor component,illustrated as magnified region 802. Upon heating (e.g., whereby theprinted structure is heated after it has been exposed to the coatingfluid), the structure of the structural precursor component can bemodified. For example, as illustrated in FIG. 8, the metal precursorcomponent can be reduced to colloidal metal particles within the polymergel by heating the mixture of the polymer gel, the porogenic solvent,and the metal precursor. This heating step facilitates reducing themetal precursor to the colloidal metal particles to form a structurehaving composite regions 804. A further heat treatment can be used todecompose the polymer gel of the composite regions 804 and the exteriorsurfaces of the printed structure to provide a free-standing printedproduct 808 comprising regions of a second level of porosity asillustrated in region 806.

In a representative embodiment, a silica-based printed product madeusing a printable composition comprising a pre-ceramic materialcomprising tetraethyl orthosilicate is described. In this embodiment, aporogenic solvent composition comprising water, a porogenic solvent(e.g., DMF), and the tetraethyl orthosilicate structural precursor iscombined with a polymer precursor component (e.g., polyethylene glycoldiacrylate, trimethylolpropane ethoxylate triacrylate, or a combinationthereof), an initiator (e.g., an α-hydroxyketone initiator, likeIRGACURE®), and a polymerization quenching compound (e.g., a dye, likeSUDAN® 1) to form a printable composition. In some embodiments, theamount of the pre-ceramic material can be selected to provide a desiredprinted product size. Solely by way of example, amounts of thepre-ceramic material lower than 50 uL can be used to provide small(fine) printed products, whereas an amount of the pre-ceramic materialabove 50 uL (e.g., 1 mL or more) can be used to provide larger printedproducts. In such embodiments, the amounts of the other printablecomposition components can be modified (e.g., increased or decreased) soas to provide a final printable composition that is homogenous orsubstantially homogenous. Once the printable composition has beenprinted, the printed intermediate structure can be exposed to one ormore post-processing steps, including a catalytic hydrolysis step and aheating step. Some embodiments can further comprise a cooling step. Inparticular representative embodiments, the printed intermediatestructure comprising the pre-ceramic material is exposed to a catalystto promote hydrolysis of the pre-ceramic orthosilicate material tosilica. In some embodiments, the catalytic hydrolysis step can compriseexposing the pre-ceramic material to a catalytic gas, such as NH₃ gas,which permeates the printed intermediate structure and catalyzespolymerization of the pre-ceramic material to provide asilica-containing printed intermediate structure. In yet additionalembodiments, the catalytic hydrolysis step can comprise exposing thepre-ceramic material to a catalytic solution, such as an ammoniumhydroxide solution, during the printing process. Once formed, thesilica-containing printed intermediate structure is then heated at atemperature and for a time to provide a desired level of porosity,strength, transparency, and/or size by decomposing the polymer gelformed from the polymer precursor components and porogenic solvent ofthe printable composition. Solely by way of example, exposing thesilica-containing printed intermediate structure to a temperature abovethat which promotes mobility and diffusion of the silica such thatsintering and densification may occur (e.g., 1000° C. or higher) canpromote increased sintering, which can provide a robust, transparentstructure with lower porosity. This temperature, however, can depend onthe fineness of the printed structure, the amount of silicon precursorused in the printable composition (which can dictate the overallshrinkage of the printed product at high temperature), how long theprinted intermediate structure is exposed to heat (for example, moredensification occurs at longer holding times), or any combinationthereof. Such embodiments may be desired for optics applications as theycan be optically transparent. As yet another example, exposing thesilica-containing printed intermediate structure to a temperature below1500 (e.g., 1300° C. or lower) can promote forming silica-based printedproducts that have hierarchical porosity. Additional ceramic printedproducts, such as boron carbide-based products, and methods of makingthe same, are described in the Examples section of the presentdisclosure.

VI. Methods of Use

The composition embodiments described herein can be used to make 3Dprinted products that have multiple different levels of porosity withinthe printed product's structure. The composition embodiments and printedproduct embodiments described herein are configured for use in a varietyof applications, such as catalysis, heat-transfer technologies,electrodes, sensing/remediation/separation technologies, construction,therapeutics, and the like.

In some embodiments, the composition embodiments and printed productembodiments described herein can be used as heterogeneous catalysissubstrates (e.g., pellets, packed tubes, and the like). In someembodiments, the composition embodiments can be used to make printedproduct embodiments configured for use in heat-transfer technologies,such as heat pipe wicks, heat shielding, passive cooling formicroelectronics, heat exchanger components, and the like. In someembodiments, the composition embodiments can be used to make printedproduct embodiments configured for use in electronics, such aselectrodes for use in batteries, electrochemical cells, or otherelectrochemical capacitor-type devices. In some other embodiments, thecomposition embodiments can be used to make printed product embodimentsconfigured for use as sensors (e.g., electrical and/or chemicalsensors), remediation components (e.g., water purification devices, gasscrubber devices, and the like), and/or separation devices, such asfiltration devices and the like. In yet additional embodiments, thecomposition embodiments can be used to make printed product embodimentsconfigured for use in construction, such as lightweight structuralreinforcement, noise reduction, fire protection, and the like. In yetadditional embodiments, the composition embodiments can be used to makeprinted product embodiments configured for use in medical applications,such as therapeutics. For example, printed product embodiments describedherein can be used as bone implant scaffolds, or as substrates forgrowing cell or bacteria cultures in controlled environments.

VII. Overview of Several Embodiments

Disclosed herein are embodiments of a composition, such as a printablecomposition, comprising: a structural precursor component; a polymerprecursor component; and a porogenic solvent. In some embodiments, ifthe composition comprises polyethylene glycol diacrylate,phenylbis(2,4,6-trimethylbenzoyl)phosphineoxide, 1-phenylazo-2-naphthol,and one or more of isopropanol, pentanol, hexanol, and dibutylphthalate, then the composition does not comprise silver or silvernitrate without further comprising a second metal or metal precursor; orif the composition comprises resorcinol, formaldehyde, water,polyethylene glycol diacrylate,phenylbis(2,4,6-trimethylbenzoyl)phosphineoxide, and1-phenylazo-2-naphthol, then the resorcinol, formaldehyde, and watermake up a volume % of the composition that is not, or is other than,80%; and the polyethylene glycol monomer,phenylbis(2,4,6-trimethylbenzoyl)phosphineoxide, and1-phenylazo-2-naphthol make up a volume % of the composition that isnot, or is other than 20%.

In any or all of the above embodiments, the structural precursorcomponent comprises a metal or a metal precursor; a polymer or a monomerprecursor to the polymer; a pre-ceramic material; a pre-metal oxide; acarbonaceous material or a precursor thereof; or any combinationsthereof.

In any or all of the above embodiments, the metal is selected fromsilver, gold, nickel, copper, iron, palladium, platinum, zinc, or acombination thereof and wherein the metal precursor is a silver salt, agold salt, a nickel salt, a palladium salt, a platinum salt, a coppersalt, an iron salt, a zinc salt, or any combinations thereof; themonomer precursor to the polymer is an imide monomer, an acrylonitrilemonomer, a dicyclopentadiene monomer, a benzoxazine monomer, or anycombinations thereof; the pre-ceramic material comprises silicon,titanium, boron, aluminum, zirconium, or any combinations thereof; thepre-metal oxide comprises a titanium oxide precursor, a cobalt oxideprecursor, a zirconium oxide precursor, a nickel oxide precursor, a tinoxide precursor, or a combination thereof; the carbonaceous material isgraphene, graphite, amorphous carbon, or any combinations thereof;and/or the precursor to the carbonaceous material is resorcinol andformaldehyde.

In any or all of the above embodiments, the polymer precursor componentcomprises a monomer unit having one or more polymerizable functionalgroups selected from a double bond, an epoxide, an alkylene oxide, anisocyanate, and the like.

In any or all of the above embodiments, the polymer precursor componentis trimethylolpropane ethoxylate triacrylate, divinyl benzene, divinylsulfone, divinyl oxybutane, polyethylene glycol diacrylate, polyesteracrylate, urethane acrylate, epoxy methacrylate, or any combinationsthereof.

In any or all of the above embodiments, the porogenic solvent isdimethylformamide, DMSO, water, an alcohol, a hydrocarbon, a weak acid,a weak base, or a combination thereof.

In any or all of the above embodiments, the composition furthercomprises a polymerization quenching compound, a reducing agent, aninitiator, or any combinations thereof.

In any or all of the above embodiments, the composition comprises theinitiator and the polymerization quenching compound, wherein theinitiator is bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide and thepolymerization quenching compound is an azo-containing dye.

In any or all of the above embodiments, the composition comprisesdimethylformamide, silver nitrate, HAuCl₄, polyethylene glycoldiacrylate, bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide, and1-phenylazo-2-naphthol.

In any or all of the above embodiments, the composition comprisesdimethylformamide, tetraethyl orthosilicate, polyethylene glycoldiacrylate, trimethylolpropane ethoxylate triacrylate,bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide, and1-phenylazo-2-naphthol.

In any or all of the above embodiments, the composition comprisesphenxoyethyl acrylate, polyethylene glycol diacrylate, DMSO, boric acid,bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide, and1-phenylazo-2-naphthol.

Also disclosed herein are embodiments of method for making a printedproduct, comprising: providing a printable composition according to thepresent disclosure and/or any or all of the composition embodimentsdescribed above; printing a printed intermediate structure with thecomposition by using a 3-D printer or other stereolithographic processto deposit layers of the composition and exposing the layers to anenergy source to polymerize the polymer precursor component of thecomposition to thereby form a polymer gel; heating the printedintermediate structure at a temperature and for a time sufficient topromote a chemical change in the structural precursor component and/orto decompose the polymer gel; and removing decomposed polymer gel fromthe structure to provide the printed product.

In any or all of the above embodiments, heating the structure at atemperature and for a time sufficient to promote chemical changes in thestructural precursor component and/or to decompose the polymer gelcomprises (i) a first heating step wherein the structure is heated topromote reduction of the structural precursor component and a secondheating step wherein the structure is heated to decompose the polymer;or (ii) a single heating step wherein the structural precursor componentis reduced and the polymer gel decomposes.

In any or all of the above embodiments, the method further comprisesexposing the printed intermediate structure to a vapor-phase reagent, agas-phase reagent, a catalyst, or a combination thereof to promote achemical change in the structural precursor component.

In any or all of the above embodiments, removing decomposed polymer gelfrom the structure to provide the printed product comprises exposing thestructure to flowing air during or after heating.

In any or all of the above embodiments, the method further comprisesexposing the structure to a coating fluid prior to heating the structureand/or rinsing the structure with a rinsing composition.

In any or all of the above embodiments, the coating fluid is an oilcapable of preventing evaporation of the porogenic solvent and/or iontransport of ions formed during heating.

In some embodiments, the method comprises: mixing a compositioncomprising an initiator, a polymerization quenching compound, and aporogenic solvent with a polymer precursor to form a first mixture;adding a solution comprising a metal precursor and water to the firstmixture to provide a second mixture; printing a printed intermediatestructure with the second mixture using a 3-D printer or otherstereolithographic process to deposit layers of the second mixture andexposing the layers to an energy source to polymerize the polymerprecursor component to thereby form a polymer gel; rinsing the printedintermediate structure with a rinsing solution comprising the porogenicsolvent and a stabilizing component; heating the printed intermediatestructure at a temperature and for a time sufficient to promote chemicalchanges in the metal precursor component and/or to decompose the polymergel; and removing decomposed polymer gel from the printed intermediatestructure to provide the printed product.

Also disclosed herein are embodiments of a printed product, comprising acombination of macroscale pores and/or channels and microscale poresand/or channels; or a combination of macroscale pores and/or channelsand nanoscale pores and/or channels; or a combination of microscalepores and/or channels and nanoscale pores and/or channels; or acombination of macroscale pores and/or channels, microscale pores and/orchannels, and nanoscale pores and/or channels, wherein the printedproduct comprises a metal other than silver, a metal alloy, a ceramicmaterial, a polymer, a metal oxide, a carbonaceous material, or anycombination thereof; and wherein the macroscale pores and/or channels,the microscale pores and/or channels, and/or the nanoscale pores and/orchannels are formed throughout the printed product.

In some embodiments, the structural component comprises a combination ofsilver and gold; gold; silica; iron; copper; boron carbide; resorcinol;or a combination thereof.

VIII. Examples Example 1

In this example, a representative method for making a 3-D printedhierarchical silver foam material is described. In this example,Solutions A-C are prepared and mixed in the particular order describedbelow.

Solution A:

100 mg of Bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide and 18 mg ofSUDAN® 1 dye are dissolved in 20 mL of dimethylformamide (DMF). Thephosphine oxide acts as a radial initiator for polymerization and thedye acts as a polymerization quenching compound to control the thicknessof printed layers and to prevent polymerization from occurring outsidethe exposed regions for each printed cross-section. The DMF acts as aporogenic solvent to produce a polymeric gel, and a robust reducingagent for silver ions that are incorporated into the printablecomposition (see solution C).

Solution B:

Solution of ethoxylated (3) trimethylolpropane triacrylate (neat).

Solution C:

A solution containing silver nitrate and deionized water, wherein 2grams of dissolved silver nitrate is used for every 1 mL of deionizedwater.

Solution D:

A 75:25 (by volume) mixture of DMF and 10% w/w polyvinylpyrrolidone(PVP) dissolved in deionized water.

Printable Composition Preparation:

The printable composition comprises 57.1% Solution A, 28.5% Solution B,and 14.4% Solution C by volume. In this example, 3.5 mL of printablecomposition is prepared by mixing 2 mL Solution A, 1 mL Solution B, and0.5 mL Solution C. As Solution C is only miscible with Solution B in thepresence of Solution A, Solutions A and B are first mixed together,followed by the addition of Solution C. This order of addition can, insome embodiments, prevent formation of an emulsion that results in phaseseparation.

Printing:

The printable composition is then loaded into a vat-typestereolithography 3-D printer and models are printed using optimizedsettings specific to each model and/or printing device. The printerspecifications (e.g., light source type and intensity; bottom-up ortop-down orientation of the printer, etc.) can be tuned/modified asneeded. In this example, the hierarchical foam material is made bychoosing a printing models that has intrinsic porosity (e.g., lattices,gyroid structures, and other porous models). Immediately after printingthe large-scale, resulting pores formed from the printing can still befilled with excess printable composition due to capillary action, andthe walls of the printed structure can be coated with excess printablecomposition. In some embodiments, the printed models are briefly“wicked” of their excess printable composition by placing them on aKimwipe or similar material to drain the larger pores of their excessnon-polymerized fluid. Then, the structures are briefly rinsed with aSolution D, described above.

The amount of solution D used to rinse the structures depends on themodel size, shape and porosity. Solely by way of example, for a 1 cm³printed model with printed pores that are ˜250 μm in diameter, roughly1-2 mL of solution D is deposited on the printed model (sitting on aKimwipe) such that it passes through the structure and rinses the wallsof uncured monomer. A rinsed printed structure is shown in the left-mostimage of FIG. 9. The PVP also acts as a stabilizer for silvernanoparticles that restricts their growth but only on the outer surfacesof the printed model (that is, not within the gel phase).

After rinsing, the structures are placed in vials to which sufficientsilicone oil (or another compatible oil) is then added to cover thestructure entirely and fill the pores of the printed structure. The oilis not miscible with the remaining fluids within the polymeric gel (e.g.DMF/water) and therefore acts as a “liquid shrink-wrap” for the porousprinted structures and thus can prevent solvent evaporation or iontransport from the inner regions of the walls to the outer surfaces. Thevial is then sealed and placed in an oven to carry out the reduction ofsilver ions by DMF and water. The temperature can be 70° C. and the vialis left in the oven for at least 4 hours.

After the reduction of silver ions is completed within the polymer gelstructure, the silicone oil in the vial along with the remaining fluidwithin the structures (this would now be residual DMF/water plus anyby-products of the silver reduction reaction described above) areexchanged with ethanol, and the structures are then dried at roomtemperature. A dried structure is shown in the middle image of FIG. 9.

To produce the metallic foams, the polymer is decomposed and the silverparticles are sintered to produce a freestanding structure. The printedstructures are placed in a furnace operating under flowing inert gas(Ar, N₂, etc.). A typical furnace program is to ramp from roomtemperature to 475° C. at a rate of 2° C./min. Then, while still at 475°C., the inert gas is shut off and the flowing gas is switched over toair, which removes any remaining carbon products from the polymer matrixto produce silver structures free of chemical contaminants. A digitalimage of a silver foam is shown in the right-most image of FIG. 9.Scanning electron microscopy images clearly show two distinct porenetworks, one from the printed structure itself, and a smallersponge-like network from the structural inversion of the polymer gelphase by sintered silver nanoparticles.

Example 2

In this example, a third level of structural hierarchy is achieved bybeginning with a silver-filled composite structure obtained from theprocedure described above for Example 1, which is rinsed thoroughly withethanol and dried at room temperature. This structure is then placed ina vial containing a Solution E, which comprises 50 mg of dissolvedHAuCl₄ per 1 mL ethanol, water, or a combination thereof. The volume ofsolution E is optimized to completely immerse the structure in solutionand wet all of the internal surfaces of the object. The structure isleft in the solution for 16 hours or more, during which goldnanoparticles are deposited within the walls and onto the internalsurfaces of the structure. The structures are again rinsed in ethanoluntil the effluent liquid is colorless, and again dried at roomtemperature. Then, the composite Au/Ag/polymer structures are placed ina tube furnace using a similar protocol as described above in Example 1.Finally, the silver component of the alloy is removed by placing themetal alloy in concentrated HNO₃ to leach the silver out of thestructure and produce nanoporous gold. This last nanoscale structure iseven smaller than the polymeric gel phase, and therefore three levels ofporosity are present in these materials: (1) the printed structure, (2)the inverse replica of the polymeric gel phase, and (3) interconnectednanopores from de-alloying of the Au/Ag alloy (see FIG. 2).

An additional example of a gold printed product is shown in FIGS.10A-10F. FIG. 10A shows a trimodal porous gold printed product and FIG.10B shows the printed product after being incorporated into aflow-through reactor for catalysis. FIGS. 10C-10F are SEM images of thegold printed product that show that the hierarchical porous network ofthe product is continuous and accessible from the bulk void volume withno discontinuities or blockage of the pores.

Example 3

In this example, a carbonaceous precursor material is used to form acarbon-based printed product. To make the printed product, 25% by volumepoly(ethylene glycol) diacrylate (e.g., MW 250) is combined with 75% byvolume water and formaldehyde solution with dissolved resorcinol. Theinitiator/absorber (SUDAN® 1) concentration relative to mass of thepolymer precursor component (i.e., poly(ethylene glycol) diacrylate) is1% and 0.18%, respectively. Using a similar processing procedure asdescribed herein, the resorcinol/formaldehyde solution and water arereacted so as to form the carbonaceous material upon heating. Alsoduring heating (or by using higher temperatures in a subsequent heatingstep), the PEG-containing polymer is decomposed to provide the freestanding printed product made of the carbonaceous material.

Example 4

In this example, a metal oxide-based printed product is made. Aconcentrated amount of cobalt nitrate is used as a pre-metal oxidematerial and, after printing a printable composition comprising thecobalt nitrate, as well as a polymer precursor component, the resultingprinted intermediate structure is heated in air to first produce cobaltoxide (e.g., at 100° C.) and then heating in air is continued at highertemperatures (e.g., 400° C.) to remove the polymer gel and produce thecobalt oxide replica.

Example 5

In this example, a hierarchical silica-based printed product was made. Aporogenic solvent comprising a combination of 1 mL H₂O, 2 mL DMF, and300 uL tetraethylorthosilicate was prepared. To this solvent mixture wasadded 3 mL PEG diacrylate and 1 mL trimethylolpropane ethoxylatetriacrylate, 20 mg IRGACURE® 819, 3.6 mg SUDAN® 1. In some embodiments,the amount of tetraethylorthosilicate can be varied widely to controlthe amount of shrinkage during the heating step. For example, when avery fine structure is desired as the final product, 50 uL or less ofTEOS is added. When a larger structure is desired, 1 mL or more TEOS isadded. In one example, 10 mg IRGACURE®, 1.8 mg SUDAN® 1, 1 mL DMF, 1.5mL PEG diacrylate, and 1.5 mL TEOS was used. The other solvent amountscan be adjusted to ensure that the final printable composition is fullymixed and homogeneous.

After printing printed intermediate structure with the above-describedcomposition, the printed intermediate structure was placed in a chamberfilled with NH₃ gas and allowed to rest for 12 hours. The gas permeatedthe part, catalyzing the polymerization of TEOS to yield silica.

Next, the printed intermediate structure was heated in a tube furnacefrom room temperature to 300° C. over 4 hours, then to 1000° C. over 5hours. The furnace was then shut down and allowed to cool naturally,providing the silica-based printed product. The silica-based ceramicprinted product is shown in FIGS. 11A-11E. FIG. 11A shows a freestandingsilica product made using an embodiment of the method discussed above.FIGS. 11B and 11C are expanded views of the product in FIG. 11A, showingthe macro-sized pores of the product. FIGS. 11D and 11E show finer poresformed in the printed product, which provide a second level of porositythat exists on length scales smaller than the macro-sized pores.

Example 6

In this example, a boron carbide-based hierarchically porous printedstructure was made. A printable composition comprising 1 mLtrimethylolpropane triacrylate, 1 mL phenoxyethyl acrylate, 1 mL PEGdiacrylate, 5.5 mL saturated DMSO solution of boric acid, 500 uL DMSO,20 mg IRGACURE®, and 5.4 mg SUDAN® 1. An object was printed with theprintable composition using a 3-D printer and was dried of any excessliquid printable composition and subjected to the follow heat treatmentsteps: (i) exposure to an initial temperature of 100° C., with rampingup to 200° C. over 12 hours under N₂; (ii) exposure to an initialtemperature of 200° C., with ramping up to 500° C. over 5 hours underN₂; (iii) holding at a temperature of 500° C. for 48 hours under N₂;then (iv) a temperature ramping step where the temperature was quicklyincreased 5-10° C./min to 1000° C. under air; (v) holding at atemperature of 1000° C. for 2 hours; (vi) exposure to nitrogen at 1000°C. for another 3 hours; and (vii) a cooling step under nitrogen. Theprinted product of this example is shown in FIG. 12 and FIG. 13 providesthe XRD pattern for the printed product obtained from using X-raydiffraction analysis on a pulverized sample of the printed product.

Example 7

In this example, another boron carbide-containing hierarchically porousprinted object was made. First, a hierarchical porous printed polymerproduct was made as described in Example 6. In particular, the printedpolymer product was formed using a printable composition comprising 10mg IRGACURE®, 1.8 mg SUDAN® 1, 0.5 mL water, and 1 mL of PEGDA MW 600.The polymer product was then soaked in a solution of boric acid-sucroseester in DMF, which was prepared by heating 3 mL DMF with 1 g boric acidand 800 mg sucrose at 100° C. until the solution was black and viscous.After soaking the printed intermediate structure in this solution forseveral days, the printed intermediate structure was fired to give aboron-carbide containing composite material. This example can bemodified to control the amount of carbon present in the final product bymodifying the heating program. For example, the printed intermediatestructure can be exposed to a high temperature environment for asuitable period of time in the presence of oxygen to provide reducedamounts of carbon-based polymer gel present in the printed product.

Example 8

In this example, a method for making a copper-based printed product isdescribed. A printed intermediate structure comprising a polymer formedfrom a polymer precursor component was soaked in a saturated watersolution of ascorbic acid overnight and then soaked in a saturatedethanol solution of copper chloride for 24 hours. The printedintermediate structure was then dried, either via evaporation,freeze-drying, or supercritical drying, and fired to remove the polymergel. In some embodiments of this example, gas flow and temperature werecontrolled to ensure that the copper particles sinter together beforeoxidizing, and that the copper was not oxidized to the point that thestructure of the part is compromised. Forming gas may be used in someexamples to reduce the copper at desirable intervals. Images of theprinted product formed from this example are provided in FIGS. 14A and14B, wherein FIG. 14A is an SEM image of the printed product on a 200 μmscale and FIG. 14B is an SEM image of the printed product on a 5 μmscale

Example 9

In this example, a method of making an iron-based printed product isdescribed. A printed intermediate structure comprising a polymer formedfrom a polymer precursor component was soaked in a saturated watersolution of iron nitrate and then dried via evaporation, freeze dryingor supercritical drying to remove any liquid solvent and then firedaccording to the following program: (i) increasing the temperature from30° C. to 500° C. over 5 hours in nitrogen; holding at 500° C. for 1hour in nitrogen; holding at 500° C. for 5 hours in air; increasing thetemperature from 500° C. to 800° C. over 1 hour in forming gas; andholding the temperature at 800° C. for 6 hours in forming gas. An imageof the printed product from this example is shown in FIG. 15A and FIGS.15B and 15C provide SEM images of pores of the product on a 200 μm scaleand 10 μm scale, respectively.

In view of the many possible embodiments to which the principles of thepresent disclosure may be applied, it should be recognized that theillustrated embodiments are only preferred examples and should not betaken as limiting the scope of the present disclosure. Rather, the scopeis defined by the following claims. We therefore claim as our inventionall that comes within the scope and spirit of these claims.

We claim:
 1. A composition, comprising dimethylformamide, silver nitrate, HAuCl₄, polyethylene glycol diacrylate, bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide, and 1-phenylazo-2-naphthol.
 2. The composition of claim 1, wherein the composition further comprises dimethyl sulfoxide (DMSO), water, an alcohol, a hydrocarbon, a weak acid, a weak base, or a combination thereof.
 3. The composition of claim 1, wherein the composition further comprises a reducing agent.
 4. A composition, comprising dimethylformamide, tetraethyl orthosilicate, polyethylene glycol diacrylate, tri methylolpropane ethoxylate triacrylate, bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide, and 1-phenylazo-2-naphthol.
 5. The composition of claim 4, wherein the composition further comprises dimethyl sulfoxide (DMSO), water, an alcohol, a hydrocarbon, a weak acid, a weak base, or a combination thereof.
 6. A composition of claim 1, comprising phenoxyethyl acrylate, polyethylene glycol diacrylate, dimethyl sulfoxide (DMSO), boric acid, bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide, and 1-phenylazo-2-naphthol.
 7. The composition of claim 6, wherein the composition further comprises dimethylformamide, water, an alcohol, a hydrocarbon, a weak acid, a weak base, or a combination thereof. 